The present invention relates to a power measuring device for use with a bicycle or other device that is powered by user operation of a pedal assembly and more particularly, to a power meter disposed within the cassette of a rear wheel assembly of a bicycle that measures the torque placed on the rear wheel assembly to determine the amount of power exerted by the user during operation of the pedal assembly.
Bicycles, stationary trainers and fixed spinner bikes outfitted with a device used to sense or detect torque and/or power are generally known. One exemplary power meter is the POWERTAP, commercially available from Saris Cycling Group, Inc. of Madison, Wis. Another representative power meter is described in U.S. Pat. No. 6,418,797 to Ambrosina et al., the disclosure of which is incorporated herein by reference. The power meter described in the '797 patent is designed to measure the torque applied to the rear hub of the cycle. The applied torque measurements together with angular velocity measurements are then used to calculate power in a manner understood by those in the art and thus provide an indication of the work exerted by a user to pedal the bicycle, trainer, etc.
To measure the torque applied to the rear hub or rear wheel assembly of the bicycle, a torque coupling member is typically mounted to the rear hub or forms part of the rear hub itself. Strain gauges or other torque sensing devices are mounted to the rear hub and in communication with the torque coupling member such that any torque experienced by the torque coupling member is detected by the strain gauges. The output of the strain gauges is then fed to a processing device that together with angular velocity information, calculates power information that can be displayed suitably to the user together with other information, such as speed, distance traveled, etc.
Electronics for the measurement of the strain, torque, power and angular velocity measurements are generally mounted in the rear hub assembly as well. The electronics include a battery for powering the electronics as well as circuitry configured to process, amplify, and convert the associated data. A radio frequency (RF) transmitter or the like is provided for transmitting the collected data to a receiver for further processing, which is typically mounted to the handlebars of the bicycle.
One of the drawbacks of conventional hub-based power meters is that it is difficult and time consuming to remove and install the torque sensing components, thereby limiting a user's ability to transfer the power meter between bicycles. That is, for a user to utilize the power meter with more than one bicycle or wheel, the user must disassemble the entire wheel including the spokes and hub. As it is common for bicyclists to utilize different types of bicycles for different types of races, events, or training environments, a great deal of time may be consumed by having to disassemble the wheel structure of one wheel such that the hub assembly incorporating the torque sensor may be used with another bicycle. Further, it can be cost-prohibitive to outfit each bicycle with a power meter when only one bicycle is being used at a time. In addition, it is difficult for a manufacturer of a hub-based power meter to provide a power meter that can be used with all or a majority of the various rear wheel configurations that are available.
The present invention is generally directed to an apparatus and method for measuring torque and/or power in a driven wheel of a pedal operated device such as a bicycle. In one representative embodiment, the invention includes a torque sensing device positioned within a hollow rear cassette. The torque sensing element may include a tube having at least one strain gauge positioned thereon. Alternatively, the torque sensing element may include a bending beam configured to detect the torque applied to the freehub of the bicycle The torque may be measured by a force sensing device connected to the bending beam or, in one alternate embodiment, disposed between a pair of orthogonally arranged bending beams.
The torque sensing elements are in communication with electronics configured to process the collected torque data for calculation of the power being applied by the user. A transmitter such as a RF transmitter may be provided in communication therewith to transmit the data in real-time to a receiver. The electronics and transmitter are preferably contained in the hollow portion of the rear cassette.
It is therefore an object of the present invention to provide a torque sensing device that is selectively interchangeable from bike-to-bike and/or wheel-to-wheel. It is yet another object of the present invention to provide a device powered by user operation of a pedal assembly that includes a torque sensing device that is relatively lightweight. It is yet another object of the present invention to provide a cost effective torque sensing system.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.